The present invention relates to a protection device according to the preamble of claim 1 below, a brake arrangement according to the preamble of claim 2 below, and a vehicle provided with such a device or brake arrangement, and a method for controlling the temperature of a brake according to the preamble of claim 13 below.
Various types of plant vehicles, such as frame-steered vehicles referred to as dumper vehicles, are conventionally provided with two different brake systems. One of the brake systems is referred to as the service brake, by means of which the vehicle can be braked, as necessary, in order to reduce the speed of the vehicle and/or to bring the vehicle to a standstill. The service brake, which may be a disk brake, is designed to be capable of delivering different braking effects within a given range depending on the load. In addition to the service brake, a further brake system, a so-called retarder, may be used in order to brake the vehicle on downgrades.
The retarder, which functions as a basic brake so that the vehicle does not reach an uncontrolled speed when the vehicle is being driven down inclines, especially long downgrades, is capable of absorbing relatively large amounts of energy for a relatively low braking effect (low braking effect over a long period of time).
Hitherto known retarders are based, for example, on the principle of restricting a flow. For example, the flow of exhaust gas in a diesel engine may be restricted in order to produce a pressure drop leading to the desired braking effect. Another way of producing a retarder is to provide some part of the transmission system with a bladed impeller, which rotates with this part, said bladed impeller being braked in that as it rotates it is compelled to displace oil.
More recently, however, another type of brake has been developed which uses the aforementioned service brake for both of the braking functions, that is to say one and the same brake system is used both for conventional braking and for retarder braking. One problem with the new use of the conventional service brakes as retarder is that they are at risk of becoming far too hot in retarder braking, or in retarder braking followed by subsequent conventional braking.
The U.S. Pat. No. 6,030,314 describes a method for braking a vehicle. According to the method the speed of a vehicle is controlled on the basis of the temperature of the brake coolant in such a way that when a temperature in excess of a predefined temperature range is registered, the brake force in retarder braking is increased in order to reduce the basic speed of the vehicle. The basic speed is further reduced until the temperature drops to such a degree that it lies within the desired temperature range. It is asserted here that increasing the brake force reduces the speed of the vehicle and hence also the amount of heat that has to be removed from the brake disks, so that the temperature of the coolant will therefore also be reduced. There are probably situations, however, in which such a method is unsuitable, and there is a risk of the brake overheating, which means that the required braking effect cannot be achieved or that the brake will be damaged, which in the long run constitutes a safety risk.
It is desirable to provide a protection device and a brake arrangement of the type described in the introductory part, which under certain, given conditions are capable of ensuring that a brake does not reach a temperature in excess of a given level, in order thereby to safeguard the working of the brake.
According to an aspect of the invention, a brake arrangement comprises a brake which is cooled by a coolant and is intended for a vehicle, the brake having a first active state in which a brake pressure is established in the brake for braking of the vehicle, a sensor for measuring the temperature of the coolant of the brake, and a control arrangement interacting with the temperature sensor and the brake in order to reduce the brake pressure of the brake in the first active state if a temperature of the coolant is in excess of a predefined value. The brake has a second active state for braking of the vehicle, in which second state the brake pressure of the brake is independent of the brake pressure reducing control arrangement, and the brake in the second active state is designed to provide a service brake function of the vehicle.
By providing the protection device/the brake arrangement with a sensor for measuring the temperature of the brake coolant, and a means interacting with the temperature sensor and the brake in order to reduce or remove the brake pressure of the brake in said first active state in the event of a temperature of said coolant in excess of a predefined value, it can be ensured that the brake is used in such a way that it is not overloaded and does not reach an undesirably high temperature.
It is desirable to provide a method of the type described in the introductory part, which under certain, given conditions is capable of ensuring that a brake does not reach a temperature in excess of a given level, in order thereby to safeguard the working of the brake.
According to another aspect of the invention, a method for controlling the temperature of a brake cooled by a coolant and arranged in a vehicle comprises operating the brake in a first active state, comprising establishing a first active state brake pressure in the brake for braking of the vehicle, measuring a temperature of the coolant of the brake, and reducing the first active state brake pressure of the brake if a temperature of the coolant is in excess of a predefined value. The method further comprises operating the brake in a second active state, comprising establishing a second active state brake pressure, the second active state brake pressure being independent of the first active state brake pressure reducing function in the first state, and wherein, in the first active state, the brake is used for braking the vehicle and, in the second active state, the brake is used for a service brake function of the vehicle.
A method according to an aspect of the invention provides a brake function which is protected against thermal overload, the method being especially suited to use in retarder braking of a vehicle which has a brake system that combines both a retarder function and a service brake function.
Aspects of the invention also relate to a vehicle provided with a protection device or brake arrangement according to the invention.